201
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Liu JP, Laufer E, Jessell TM. Assigning the positional identity of spinal motor neurons: rostrocaudal patterning of Hox-c expression by FGFs, Gdf11, and retinoids. Neuron 2001; 32:997-1012. [PMID: 11754833 DOI: 10.1016/s0896-6273(01)00544-x] [Citation(s) in RCA: 228] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Subclasses of motor neurons are generated at different positions along the rostrocaudal axis of the spinal cord. One feature of the rostrocaudal organization of spinal motor neurons is a position-dependent expression of Hox genes, but little is known about how this aspect of motor neuron subtype identity is assigned. We have used the expression profile of Hox-c proteins to define the source and identity of patterning signals that impose motor neuron positional identity along the rostrocaudal axis of the spinal cord. We provide evidence that the convergent activities of FGFs, Gdf11, and retinoid signals originating from Hensen's node and paraxial mesoderm establish and refine the Hox-c positional identity of motor neurons in the developing spinal cord.
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Affiliation(s)
- J P Liu
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Biophysics, Columbia University, 701 West 168th Street, New York, NY 10032, USA
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202
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Abstract
ETS-domain transcription-factor networks represent a model for how combinatorial gene expression is achieved. These transcription factors interact with a multitude of co-regulatory partners to elicit gene-specific responses and drive distinct biological processes. These proteins are controlled by a complex series of inter and intramolecular interactions, and signalling pathways impinge on these proteins to further regulate their action.
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Affiliation(s)
- A D Sharrocks
- School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester, M13 9PT, UK.
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203
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Chotteau-Lelievre A, Dolle P, Peronne V, Coutte L, de Launoit Y, Desbiens X. Expression patterns of the Ets transcription factors from the PEA3 group during early stages of mouse development. Mech Dev 2001; 108:191-5. [PMID: 11578874 DOI: 10.1016/s0925-4773(01)00480-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
erm, er81 and pea3 are three related genes that define a novel Ets-related subfamily of transcription factors. The expression patterns of these genes has been previously characterized in the mouse from embryonic day (E) 9.5 to birth (Oncogene 15 (1997) 937). In this study, we report differential expression patterns of the PEA3 group genes during early mouse post-implantation development. erm and pea3 expression patterns were partly overlapping. erm was activated prior to pea3 in the distal tip of the embryonic epiblast but, at primitive streak-stages, both genes were coexpressed in the posterior region of the embryo in epiblast, primitive streak and adjacent mesoderm. Similar erm and pea3 expression patterns were seen later in posterior neural plate, presomitic and lateral mesoderm, mesonephros, and tail bud. Only erm, however, was expressed in specific brain regions corresponding to prospective midbrain and ventral forebrain. erm was also strongly expressed as early as E8 in the developing branchial region, especially at the level of branchial pouches, whereas pea3 transcripts appeared later in frontonasal and first arch mesenchyme. er81 transcripts were not detected prior to E9.0-9.5, suggesting that this gene may not be involved in early developmental events.
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Affiliation(s)
- A Chotteau-Lelievre
- Mécanismes du Développement et de la Cancérisation, UMR 8526 CNRS/Institut Pasteur de Lille - Institut de Biologie de Lille, 1 rue Calmette, BP 447, 59021 Lille Cedex, France.
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204
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Raible F, Brand M. Tight transcriptional control of the ETS domain factors Erm and Pea3 by Fgf signaling during early zebrafish development. Mech Dev 2001; 107:105-17. [PMID: 11520667 DOI: 10.1016/s0925-4773(01)00456-7] [Citation(s) in RCA: 186] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Several molecules of the Fibroblast growth factor family have been implicated in the development of the vertebrate brain, but the effectors of these molecules remain largely unknown. Here we study Erm and Pea3, two ETS domain transcription factors, and show that their expression correlates closely with the domains of fgf8 and fgf3 expression. In situ hybridization analysis in wild-type and acerebellar (ace) mutant embryos defective for fgf8 demonstrates a requirement of Fgf8 for normal expression levels of erm and pea3 transcripts in and close to various domains of Fgf8 action, including the prospective midbrain-hindbrain region, the somites, the neural crest, the forebrain, and developing eyes. Morpholino-oligomer-assisted gene knock-down experiments targeted against fgf8 and fgf3 suggest that Fgf3 and Fgf8 are co-regulators of these genes in the early forebrain anlage. Furthermore, inhibition of Fgf signaling by overexpression of sprouty4 or application of the Fgf inhibitor SU5402 leads to a loss of all erm and pea3 expression domains. Conversely, ectopically provided fgf3 mRNA or implanted beads coated with Fgf8 elicit ectopic transcription of erm and pea3. Both activation and loss of transcripts can be observed within short time frames. We conclude that both the transcriptional onset and maintenance of these factors are tightly coupled to Fgf signaling and propose that erm and pea3 transcription is a direct readout of cells to Fgf levels. Given the knowledge that has accumulated on the posttranslational control of ETS domain factors and their combinatorial interactions with other transcription factors, we suggest that the close coupling of erm and pea3 transcription to Fgf signaling might serve to integrate Fgf signaling with other signals to establish refined patterns in embryonic development.
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Affiliation(s)
- F Raible
- Max-Planck-Institute for Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
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205
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Sarafi-Reinach TR, Melkman T, Hobert O, Sengupta P. The lin-11 LIM homeobox gene specifies olfactory and chemosensory neuron fates in C. elegans. Development 2001; 128:3269-81. [PMID: 11546744 DOI: 10.1242/dev.128.17.3269] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Chemosensory neuron diversity in C. elegans arises from the action of transcription factors that specify different aspects of sensory neuron fate. In the AWB and AWA olfactory neurons, the LIM homeobox gene lim-4 and the nuclear hormone receptor gene odr-7 are required to confer AWB and AWA-specific characteristics respectively, and to repress an AWC olfactory neuron-like default fate. Here, we show that AWA neuron fate is also regulated by a member of the LIM homeobox gene family, lin-11. lin-11 regulates AWA olfactory neuron differentiation by initiating expression of odr-7, which then autoregulates to maintain expression. lin-11 also regulates the fate of the ASG chemosensory neurons, which are the lineal sisters of the AWA neurons. We show that lin-11 is expressed dynamically in the AWA and ASG neurons, and that misexpression of lin-11 is sufficient to promote an ASG, but not an AWA fate, in a subset of neuron types. Our results suggest that differential temporal regulation of lin-11, presumably together with its interaction with asymmetrically segregated factors, results in the generation of the distinct AWA and ASG sensory neuron types. We propose that a LIM code may be an important contributor to the generation of functional diversity in a subset of olfactory and chemosensory neurons in C. elegans.
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Affiliation(s)
- T R Sarafi-Reinach
- Department of Biology and Volen Center for Complex Systems, Brandeis University, MS008, 415 South Street, Waltham, MA 02454, USA
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206
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Chen ZF, Rebelo S, White F, Malmberg AB, Baba H, Lima D, Woolf CJ, Basbaum AI, Anderson DJ. The paired homeodomain protein DRG11 is required for the projection of cutaneous sensory afferent fibers to the dorsal spinal cord. Neuron 2001; 31:59-73. [PMID: 11498051 DOI: 10.1016/s0896-6273(01)00341-5] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Cutaneous sensory neurons that detect noxious stimuli project to the dorsal horn of the spinal cord, while those innervating muscle stretch receptors project to the ventral horn. DRG11, a paired homeodomain transcription factor, is expressed in both the developing dorsal horn and in sensory neurons, but not in the ventral spinal cord. Mouse embryos deficient in DRG11 display abnormalities in the spatio-temporal patterning of cutaneous sensory afferent fiber projections to the dorsal, but not the ventral spinal cord, as well as defects in dorsal horn morphogenesis. These early developmental abnormalities lead, in adults, to significantly attenuated sensitivity to noxious stimuli. In contrast, locomotion and sensori-motor functions appear normal. Drg11 is thus required for the formation of spatio-temporally appropriate projections from nociceptive sensory neurons to their central targets in the dorsal horn of the spinal cord.
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Affiliation(s)
- Z F Chen
- Division of Biology 216-76 and, Howard Hughes Medical Institute, California Institute of Technology, 91125, Pasadena, CA, USA
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207
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Jacob J, Hacker A, Guthrie S. Mechanisms and molecules in motor neuron specification and axon pathfinding. Bioessays 2001; 23:582-95. [PMID: 11462212 DOI: 10.1002/bies.1084] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The vertebrate nervous system performs the most complex functions of any organ system. This feat is mediated by dedicated assemblies of neurons that must be precisely connected to one another and to peripheral tissues during embryonic development. Motor neurons, which innervate muscle and regulate autonomic functions, form an integral part of this neural circuitry. The first part of this review describes the remarkable progress in our understanding of motor neuron differentiation, which is arguably the best understood model of neuronal differentiation to date. During development, the coordinate actions of inductive signals from adjacent non-neural tissues initiate the differentiation of distinct motor neuron subclasses, with specific projection patterns, at stereotypical locations within the neural tube. Underlying this specialisation is the expression of specific homeodomain proteins, which act combinatorially to confer motor neurons with both their generic and subtype-specific properties. Ensuring that specific motor neuron subtypes innervate the correct target structure, however, requires precise motor axon guidance mechanisms. The second half of this review focuses on how distinct motor neuron subtypes pursue highly specific projection patterns by responding differentially to spatially discrete attractive and repulsive molecular cues. The tight link between motor neuron specification and axon pathfinding appears to be established by the dominant role of homeodomain proteins in dictating the ways that navigating motor axons interpret the plethora of guidance cues impinging on growth cones.
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Affiliation(s)
- J Jacob
- MRC Centre for Developmental Neurobiology, King's College, London
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208
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Greenall A, Willingham N, Cheung E, Boam DS, Sharrocks AD. DNA binding by the ETS-domain transcription factor PEA3 is regulated by intramolecular and intermolecular protein.protein interactions. J Biol Chem 2001; 276:16207-15. [PMID: 11278941 DOI: 10.1074/jbc.m011582200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The control of DNA binding by eukaryotic transcription factors represents an important regulatory mechanism. Many transcription factors are controlled by cis-acting autoinhibitory modules that are thought to act by blocking promiscuous DNA binding in the absence of appropriate regulatory cues. Here, we have investigated the determinants and regulation of the autoinhibitory mechanism employed by the ETS-domain transcription factor, PEA3. DNA binding is inhibited by a module composed of a combination of two short motifs located on either side of the ETS DNA-binding domain. A second type of protein, Ids, can act in trans to mimic the effect of these cis-acting inhibitory motifs and reduce DNA binding by PEA3. By using a one-hybrid screen, we identified the basic helix-loop-helix-leucine zipper transcription factor USF-1 as an interaction partner for PEA3. PEA3 and USF-1 form DNA complexes in a cooperative manner. Moreover, the formation of ternary PEA3.USF-1.DNA complexes requires parts of the same motifs in PEA3 that form the autoinhibitory module. Thus the binding of USF-1 to PEA3 acts as a switch that modifies the autoinhibitory motifs in PEA3 to first relieve their inhibitory action, and second, promote ternary nucleoprotein complex assembly.
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Affiliation(s)
- A Greenall
- School of Biochemistry and Genetics, The Medical School, University of Newcastle Upon Tyne, Newcastle Upon Tyne NE2 4HH, United Kingdom
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209
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Su Z, Shi Y, Friedman R, Qiao L, McKinstry R, Hinman D, Dent P, Fisher PB. PEA3 sites within the progression elevated gene-3 (PEG-3) promoter and mitogen-activated protein kinase contribute to differential PEG-3 expression in Ha-ras and v-raf oncogene transformed rat embryo cells. Nucleic Acids Res 2001; 29:1661-71. [PMID: 11292838 PMCID: PMC31320 DOI: 10.1093/nar/29.8.1661] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2001] [Revised: 02/19/2001] [Accepted: 03/01/2001] [Indexed: 11/13/2022] Open
Abstract
Transformation of normal cloned rat embryo fibroblast (CREF) cells with cellular oncogenes results in acquisition of anchorage-independent growth and oncogenic potential in nude mice. These cellular changes correlate with an induction in the expression of a cancer progression-promoting gene, progression elevated gene-3 (PEG-3). To define the mechanism of activation of PEG-3 as a function of transformation by the Ha-ras and v-raf oncogenes, evaluations of the signaling and transcriptional regulation of the approximately 2.0 kb promoter region of the PEG-3 gene, PEG-Prom, was undertaken. The full-length and various mutated regions of the PEG-Prom were linked to a luciferase reporter construct and tested for promoter activity in CREF and oncogene-transformed CREF cells. An analysis was also performed using CREF cells doubly transformed with Ha-ras and the Ha-ras specific suppressor gene Krev-1, which inhibits the transformed phenotype in vitro. These assays document an association between expression of the transcription regulator PEA3 and PEG-3. The levels of PEA3 and PEG-3 RNA and proteins are elevated in the oncogenically transformed CREF cells, and reduced in transformation and tumorigenic suppressed Ha-ras/Krev-1 doubly transformed CREF cells. Enhanced tumorigenic behavior, PEG-3 promoter function and PEG-3 expression in Ha-ras transformed cells were all dependent upon increased activity within the mitogen-activated protein kinase (MAPK) pathway. Electrophoretic mobility shift assays and DNase I footprinting experiments indicate that PEA3 binds to sites within the PEG-Prom in transformed rodent cells in an area adjacent to the TATA box in a MAPK-dependent fashion. These findings demonstrate an association between Ha-ras and v-raf transformation of CREF cells with elevated PEA3 and PEG-3 expression, and they implicate MAPK signaling via PEA3 as a signaling cascade involved in activation of the PEG-Prom.
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Affiliation(s)
- Z Su
- Department of Urology, Department of Pathology and Department of Neurosurgery, Herbert Irving Comprehensive Cancer Center, Columbia University, College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
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210
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Powell EM, Mars WM, Levitt P. Hepatocyte growth factor/scatter factor is a motogen for interneurons migrating from the ventral to dorsal telencephalon. Neuron 2001; 30:79-89. [PMID: 11343646 DOI: 10.1016/s0896-6273(01)00264-1] [Citation(s) in RCA: 258] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Cortical interneurons arise from the proliferative zone of the ventral telencephalon, the ganglionic eminence, and migrate into the developing neocortex. The spatial patterns of migratory interneurons reflect the complementary expression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, MET, in the forebrain. Scatter assays on forebrain explants demonstrate regionally specific motogenic activity due to HGF/SF. In addition, exogenous ligand disrupts normal cell migration. Mice lacking the urokinase-type plasminogen activator receptor (u-PAR), a key component of HGF/SF activation, exhibit deficient scatter activity in the forebrain, abnormal interneuron migration from the ganglionic eminence, and reduced interneurons in the frontal and parietal cortex. The data suggest that HGF/SF motogenic activity, which is essential for normal development of other organ systems, is a conserved mechanism that regulates trans-telencephalic migration of interneurons.
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Affiliation(s)
- E M Powell
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA. epowell+@pitt.edu
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211
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Abstract
Appendages, such as wings of a fly or limbs of a vertebrate, are excellent models to study the principles of patterning and morphogenesis. In the adult these structures are used for a variety of behaviors, including locomotion. Although support structures of the adult vertebrate limb are generated within the limb bud, its dynamic elements are derived from the somitic mesoderm and neural tube. Recent studies show that regional patterns set up in the mesenchyme-filled limb bud guide muscle precursors and developing motor axons to their proper location within the limb. Subsequent development of the neuromuscular system is regulated by cell surface interactions between pre-specified muscle fibers and motor axons.
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Affiliation(s)
- K Sharma
- Department of Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, Illinois 60637, USA.
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212
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Abstract
Experiments in chick embryos using classical transplantation techniques introduced by Viktor Hamburger are reviewed; these demonstrated that chick-limb innervating motoneurons become specified by extrinsic signals prior to axon outgrowth and that they selectively grow to appropriate muscles by actively responding to guidance cues within the limb. More recent experiments reveal that fast/slow and flexor/extensor subclasses of motoneurons are distinct by E4-5 and that they exhibit patterned spontaneous activity while still growing to their targets. These observations are then related to the combinatorial code of LIM transcription factor expression, which has been hypothesized to specify motoneuron subtypes.
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Affiliation(s)
- L T Landmesser
- Department of Neurosciences, Case Western Reserve University, School of Medicine, 10900 Euclid Ave, Cleveland, OH 44106-4975, USA.
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213
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Garcès A, Livet J, Grillet N, Henderson CE, Delapeyrière O. Responsiveness to neurturin of subpopulations of embryonic rat spinal motoneuron does not correlate with expression of GFR alpha 1 or GFR alpha 2. Dev Dyn 2001; 220:189-97. [PMID: 11241828 DOI: 10.1002/1097-0177(20010301)220:3<189::aid-dvdy1106>3.0.co;2-i] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Glial cell-line derived neurotrophic factor (GDNF) and its relative neurturin (NTN) are both potent trophic factors for motoneurons. They exert their biological effects by activating the RET tyrosine kinase in the presence of a GPI-linked coreceptor, either GFR alpha 1 (considered to be the favored coreceptor for GDNF) or GFR alpha 2 (the preferred NTN coreceptor). By whole-mount in situ hybridization on embryonic rat spinal cord, we demonstrate that, whereas Ret is expressed by nearly all motoneurons, Gfra1 and Gfra2 exhibit complementary and sometimes overlapping patterns of expression. In the brachial and sacral regions, the majority of motoneurons express Gfra1 but only a minority express Gfra2. Accordingly, most motoneurons purified from each region are kept alive in culture by GDNF. However, brachial motoneurons respond poorly to NTN, whereas NTN maintains as many sacral motoneurons as does GDNF. Thus, spinal motoneurons are highly heterogeneous in their expression of receptors for neurotrophic factors of the GDNF family, but their differing responses to NTN are not correlated with expression levels of Gfra1 or Gfra2.
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Affiliation(s)
- A Garcès
- INSERM U.382, Developmental Biology Institute of Marseille, CNRS-INSERM-Université de la Méditerranée, AP de Marseille, Campus de Luminy, Case 907, 13288 Marseille Cedex 09, France
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214
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de Launoit Y, Chotteau-Lelievre A, Beaudoin C, Coutte L, Netzer S, Brenner C, Huvent I, Baert JL. The PEA3 group of ETS-related transcription factors. Role in breast cancer metastasis. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 480:107-16. [PMID: 10959416 DOI: 10.1007/0-306-46832-8_13] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The ets genes encode eukaryotic transcription factors that are involved in tumorigenesis and developmental processes. The signature of the Ets family is the ETS-domain, which binds to sites containing a central 5'-GGAA/T-3' motif. They can be sub-classified primarily because of the high amino acid conservation in their ETS-domains and, in addition, in the conservation of other domains generally characterized as transactivating. This is the case for the PEA3 group, which is currently made up of three members, PEA3/E1AF, ER81/ETV1 and ERM, which are more than 95% identical in the ETS-domain and more than 85% in the transactivation acidic domain. The members of the PEA3 group are activated through both the Ras-dependent and other kinase pathways, a function which emphasizes their involvement in several oncogenic mechanisms. The expression pattern of the three PEA3 group genes during mouse embryogenesis suggests that they are differentially regulated, probably to serve important functions such as tissue interaction. Although the target genes of these transcription factors are multiple, their most frequently studied role concerns their involvement in the metastatic process. In fact, PEA3 group members are over-expressed in metastatic human breast cancer cells and mouse mammary tumors, a feature which suggests a function of these transcription factors in mammary oncogenesis. Moreover, when they are ectopically over-expressed in non-metastatic breast cancer cells, these latter become metastatic with the activation of transcription of matrix metalloproteinases or adhesion molecules, such as ICAM-1.
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Affiliation(s)
- Y de Launoit
- UMR 8526 CNRS-Institut Pasteur, Institut de Biologie de Lille, France
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215
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Abstract
The generation of distinct classes of neurons at defined positions is a fundamental step in the development of the vertebrate central nervous system. Recent work has begun to reveal the extracellular signals and transcriptional mediators that direct the pattern of generation of distinct neuronal subtypes in the neural tube. This work has provided a framework to understand the patterning of the ventral neural tube and is permitting molecular analyses of the assembly of functional neuronal circuits.
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Affiliation(s)
- J Briscoe
- Division of Developmental Neurobiology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
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216
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Affiliation(s)
- K Sharma
- Department of Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, IL 60637, USA.
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217
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Remy P, Baltzinger M. The Ets-transcription factor family in embryonic development: lessons from the amphibian and bird. Oncogene 2000; 19:6417-31. [PMID: 11175358 DOI: 10.1038/sj.onc.1204044] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
This chapter reviews the expression and role of Ets-genes during embryogenesis of amphibians and birds. In addition to overlapping expression domains, some of them exhibit cell type-specific expression. Many of them are expressed in migratory cells: neural crest, endothelial, and pronephric duct cells for instance. They are also transcribed in embryonic areas affected by epithelio-mesenchymal transitions. Both processes involve modifications of cellular adhesion. Ets-family genes appear to coordinate changes in the expression of adhesion molecules and degradation of the extracellular matrix upon regulation of matrix metalloproteinases and their specific inhibitors. These functions are essential for physiological processes like tissue remodelling during embryogenesis or wound healing. Unfortunately they also play a harmful role in metastasis. Recent studies in the nervous system showed that Ets-genes contribute to the establishment of a cellular identity. This identity could rely on definite cell-surface determinants, among which cadherins could play an important role. In addition to cell-type specific expression, other factors contribute to the specificity of function of Ets-genes. These genes have a broad specificity of recognition of target sequences in gene promoters, insufficient for accurate control of gene expression. A fine tuning could arise from combinatorial interactions with other Ets- or accessory proteins.
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Affiliation(s)
- P Remy
- FRE 2168 du CNRS, IPCB, 21 rue René Descartes, 67084 Strasbourg cedex, France
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218
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Maroulakou IG, Bowe DB. Expression and function of Ets transcription factors in mammalian development: a regulatory network. Oncogene 2000; 19:6432-42. [PMID: 11175359 DOI: 10.1038/sj.onc.1204039] [Citation(s) in RCA: 151] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The Ets transcription factor family is involved in a variety of mammalian developmental processes at the cellular, tissue and organ levels. They are implicated in cellular proliferation, differentiation, migration, apoptosis and cell - cell interactions. This article reviews recent studies that demonstrate the integral importance of Ets in the dosage dependent regulation of development. The expression of many Ets genes is associated with mesenchymal - epithelial interactions and changes in extracellular matrix proteins. These inductive processes contribute to tissue remodeling and integrity, particularly during embryonic development. Overlapping as well as unique patterns of Ets expression are evident in developing tissues, including development of the lymphoid and myeloid lineages, brain and central nervous system, bone and mammary gland. Integration of these data will allow the development of predictive models for the regulation of complex developmental processes.
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Affiliation(s)
- I G Maroulakou
- Center for Molecular and Structural Biology, Hollings Cancer Center, Medical University of South Carolina, Charleston, South Carolina, SC 29403, USA
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219
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Gibson CL, Arnott GA, Clowry GJ. Plasticity in the rat spinal cord seen in response to lesions to the motor cortex during development but not to lesions in maturity. Exp Neurol 2000; 166:422-34. [PMID: 11085907 DOI: 10.1006/exnr.2000.7511] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Motor cortical inputs and proprioreceptive muscle afferents largely target the same spinal cord region. This study explored the idea that during development the two inputs interact via an activity-dependent mechanism to produce mature patterns of innervation. In rats, the forelimb motor cortex was ablated unilaterally at either postnatal day 7 (P7), the beginning of corticospinal synaptogenesis in the cervical cord, or at P50. Comparisons were made with sham-operated animals. At P70, muscle afferents from the extensor digitorum communis muscle, contralateral to the lesion, were transganglionically labeled with cholera toxin B-subunit. Lower cervical spinal cord sections were immunostained for cholera toxin B, parvalbumin, and cJun. Our small lesions had no obvious effects upon forelimb function. However, developmental lesions, but not adult lesions, were shown to significantly increase the number of muscle afferent boutons present in the contralateral ventral horn, compared with sham-operated controls. Also, the ratio of parvalbumin-positive neurons contralateral/ipsilateral to the developmental lesion (but not adult lesions) was decreased and the ratio of cJun-positive motoneurons increased. Thus, an early motor cortex lesion resulted in retention of a proportion of muscle afferent synapses to the ventral horn that are known to be lost during normal development. Parvalbumin and cJun are markers of neuronal activity suggesting that spinal circuitry develops permanently altered activity patterns in response to an early cortical lesion, although this plasticity is lost in the mature animal.
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Affiliation(s)
- C L Gibson
- Developmental Neuroscience Group, Newcastle University, Newcastle upon Tyne, NE1 4LP, United Kingdom
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220
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Laing MA, Coonrod S, Hinton BT, Downie JW, Tozer R, Rudnicki MA, Hassell JA. Male sexual dysfunction in mice bearing targeted mutant alleles of the PEA3 ets gene. Mol Cell Biol 2000; 20:9337-45. [PMID: 11094084 PMCID: PMC102190 DOI: 10.1128/mcb.20.24.9337-9345.2000] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PEA3, a member of the Ets family of transcriptional regulatory proteins, is expressed in a unique spatial and temporal pattern during mouse embryogenesis; its overexpression is positively correlated with HER2-mediated breast tumorigenesis in both humans and mice. To determine whether PEA3 plays a part in development and oncogenesis and to uncover its normal physiological role, we generated mice lacking functional PEA3 by gene targeting in embryonic stem cells. PEA3(-/-) mice arose from heterozygous crosses with the expected Mendelian frequency, revealing that PEA3 is dispensable for embryogenesis. PEA3 mutant mice displayed no overt phenotype and lived a normal life span. However, PEA3-deficient males failed to reproduce. PEA3 is expressed in several male sexual organs, but gross and histological analyses of the organs from PEA3(-/-) mice revealed no abnormalities. Spermatogenesis and spermiogenesis also appeared normal in mice homozygous for the PEA3 mutation, and their sperm were capable of fertilizing eggs in vitro. PEA3(-/-) males engaged in normal mating behavior, but they did not set copulatory plugs and sperm could not be detected in the uteri of females that had mated with PEA3(-/-) males. Erections could be evoked by abdominal pressure in PEA3-deficient male mice, and the results of in vitro experiments revealed that the corpus cavernosum isolated from PEA3 mutant males relaxed in response to acetylcholine. Therefore, the infertility of PEA3 mutant males involves either mechanisms proximal to the cavernosal smooth muscle or an ejaculatory dysfunction. However, PEA3 mutant mice are phenotypically distinguishable from other knockout mice with such deficits and thus provide a unique model for further investigation of male sexual dysfunction.
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Affiliation(s)
- M A Laing
- Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, Ontario, Canada L8S 4K1
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221
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Rifkin JT, Todd VJ, Anderson LW, Lefcort F. Dynamic expression of neurotrophin receptors during sensory neuron genesis and differentiation. Dev Biol 2000; 227:465-80. [PMID: 11071767 DOI: 10.1006/dbio.2000.9841] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
To identify potential functions for neurotrophins during sensory neuron genesis and differentiation, we determined the temporal and spatial protein expression patterns of neurotrophin receptors throughout the process of sensory neurogenesis in the dorsal root ganglia (DRG). We show that neurotrophin receptors are expressed early, being first detected on subsets of migrating neural crest cells, and that trkC is among the earliest markers of neural lineage specification. In the immature DRG, we find that both trkC and p75(NTR) are expressed on subsets of dividing progenitor cells in vivo. Furthermore, our data directly reveal distinct patterns of trk receptor expression by individual sensory neurons from the time of their inception with all early arising cells initially being trkC(+), some subsets of whom also coexpress either trkA or trkB or both. As sensory neurons innervate their targets and establish their mature identities, the spectrum of trk receptors expressed by individual neurons is altered. The stereotyped trk receptor expression profiles identified here may potentially correspond to distinct lineages of sensory neurons. These data, in conjunction with other studies, argue for multiple functions for neurotrophins during the process of sensory neuron differentiation, including effects on both neural crest and DRG mitotically active progenitor cells, in addition to possibly influencing the establishment of sensory neuron identity.
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MESH Headings
- Animals
- Apoptosis
- Base Sequence
- Cell Differentiation
- Chick Embryo
- DNA Primers/genetics
- Ganglia, Spinal/embryology
- Ganglia, Spinal/metabolism
- Gene Expression Regulation, Developmental
- Mitosis
- Neural Crest/cytology
- Neural Crest/metabolism
- Neurons, Afferent/cytology
- Neurons, Afferent/metabolism
- Receptor, trkA/genetics
- Receptor, trkA/metabolism
- Receptor, trkB/genetics
- Receptor, trkB/metabolism
- Receptor, trkC/genetics
- Receptor, trkC/metabolism
- Receptors, Nerve Growth Factor/genetics
- Receptors, Nerve Growth Factor/metabolism
- Stem Cells/cytology
- Stem Cells/metabolism
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Affiliation(s)
- J T Rifkin
- Biotech Services Group, 1700 Rockville Pike, Rockville, Maryland 20850, USA
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222
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Wenner P, O'Donovan MJ, Matise MP. Topographical and physiological characterization of interneurons that express engrailed-1 in the embryonic chick spinal cord. J Neurophysiol 2000; 84:2651-7. [PMID: 11068006 DOI: 10.1152/jn.2000.84.5.2651] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A number of homeodomain transcription factors have been implicated in controlling the differentiation of various types of neurons including spinal motoneurons. Some of these proteins are also expressed in spinal interneurons, but their function is unknown. Progress in understanding the role of transcription factors in interneuronal development has been slow because the synaptic connections of interneurons, which in part define their identity, are difficult to establish. Using whole cell recording in the isolated spinal cord of chick embryos, we assessed the synaptic connections of lumbosacral interneurons expressing the Engrailed-1 (En1) transcription factor. Specifically we established whether En1-expressing interneurons made direct connections with motoneurons and whether they constitute a single interneuron class. Cells were labeled with biocytin and subsequently processed for En1 immunoreactivity. Our findings indicate that the connections of En1-expressing cells with motoneurons and with sensory afferents were diverse, suggesting that the population was heterogeneous. In addition, the synaptic connections we tested were similar in interneurons that expressed the En1 protein and in many that did not. The majority of sampled En1 cells did, however, exhibit a direct synaptic connection to motoneurons that is likely to be GABAergic. Because our physiological methods underestimate the number of direct connections with motoneurons, it is possible that the great majority, perhaps all, En1-expressing cells make direct synaptic connections with motoneurons. Our results raise the possibility that En1 could be involved in interneuron-motoneuron connectivity but that its expression is not restricted to a distinct functional subclass of ventral interneuron. These findings constrain hypotheses about the role of En-1 in interneuron development and function.
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Affiliation(s)
- P Wenner
- National Institutes of Health, National Institute of Neurological Disorders and Stroke, Lab of Neural Control, Bethesda, Maryland 20892-4455, USA
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223
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Jessell TM. Neuronal specification in the spinal cord: inductive signals and transcriptional codes. Nat Rev Genet 2000; 1:20-9. [PMID: 11262869 DOI: 10.1038/35049541] [Citation(s) in RCA: 1539] [Impact Index Per Article: 64.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Neural circuits are assembled with remarkable precision during embryonic development, and the selectivity inherent in their formation helps to define the behavioural repertoire of the mature organism. In the vertebrate central nervous system, this developmental program begins with the differentiation of distinct classes of neurons from progenitor cells located at defined positions within the neural tube. The mechanisms that specify the identity of neural cells have been examined in many regions of the nervous system and reveal a high degree of conservation in the specification of cell fate by key signalling molecules.
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Affiliation(s)
- T M Jessell
- Howard Hughes Medical Institute, Center for Neurobiology and Behavior, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
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224
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Halfon MS, Carmena A, Gisselbrecht S, Sackerson CM, Jiménez F, Baylies MK, Michelson AM. Ras pathway specificity is determined by the integration of multiple signal-activated and tissue-restricted transcription factors. Cell 2000; 103:63-74. [PMID: 11051548 DOI: 10.1016/s0092-8674(00)00105-7] [Citation(s) in RCA: 256] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Ras signaling elicits diverse outputs, yet how Ras specificity is generated remains incompletely understood. We demonstrate that Wingless (Wg) and Decapentaplegic (Dpp) confer competence for receptor tyrosine kinase-mediated induction of a subset of Drosophila muscle and cardiac progenitors by acting both upstream of and in parallel to Ras. In addition to regulating the expression of proximal Ras pathway components, Wg and Dpp coordinate the direct effects of three signal-activated (dTCF, Mad, and Pointed-functioning in the Wg, Dpp, and Ras/MAPK pathways, respectively) and two tissue-restricted (Twist and Tinman) transcription factors on a progenitor identity gene enhancer. The integration of Pointed with the combinatorial effects of dTCF, Mad, Twist, and Tinman determines inductive Ras signaling specificity in muscle and heart development.
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Affiliation(s)
- M S Halfon
- Department of Medicine, Brigham and Women's Hospital, Harvard Medical School and Howard Hughes Medical Institute, Boston, Massachusetts 02115, USA
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225
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McDonough J, Francis N, Miller T, Deneris ES. Regulation of transcription in the neuronal nicotinic receptor subunit gene cluster by a neuron-selective enhancer and ETS domain factors. J Biol Chem 2000; 275:28962-70. [PMID: 10878018 DOI: 10.1074/jbc.m004181200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of neurotransmitter receptors encoded by the nicotinic acetylcholine receptor (nAchR) subunit gene cluster depends on coexpression of the beta4, alpha3, and alpha5 subunits in certain kinds of neurons. One way in which coexpression might be achieved is through the regulation of promoters in the cluster by neuron-selective enhancers. The beta43' enhancer is located between the beta4 and alpha3 promoters and it directs cell type-specific expression in cell lines. It is not known, however, whether beta43' is active in neurons. Therefore, we assayed beta43' in dissociated rat sympathetic ganglia cultures, which contain nAchR-positive neurons as well as nAchR-negative non-neuronal cells. Reporters controlled by the alpha3 promoter and beta43' were expressed in a neuron-selective manner; greater than 90% and up to 100% of luciferase expression was detected in neurons. Neuron selectivity was maintained when beta43' was placed next to ubiquitously active viral promoters. In contrast, replacing beta43' with the SV40 enhancer eliminated neuron selectivity. The enhancer is composed of at least two separate but functionally interdependent elements, each of which interacts with a different type of ETS domain factor. These findings support a model in which beta43' controls neuronal expression of one or more genes in the cluster through interactions with a combination of ETS factors.
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Affiliation(s)
- J McDonough
- Department of Neurosciences, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106, USA
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226
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Glover JC. Neuroepithelial 'compartments' and the specification of vestibular projections. PROGRESS IN BRAIN RESEARCH 2000; 124:3-21. [PMID: 10943113 DOI: 10.1016/s0079-6123(00)24004-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The implication that there exist coherent vestibulo-ocular neuron pools with specific functions may provide new insight into how conjugate eye movements are synthesized within the vestibulo-ocular reflex. The systematic relationship between pool position and synergistic principle terminations, the 'hodological mosaic' suggests, moreover, a determinate groundplan established by developmental mechanisms operative at early stages in the hindbrain neuroepithelium. From such a groundplan, evolutionary and use-dependent modifications could mold connectivity patterns functionally appropriate for each species and individual. How the expression of developmentally regulatory genes contributes to establishing the mosaic organization of the vestibular system is the current focus of our research.
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Affiliation(s)
- J C Glover
- Department of Anatomy, University of Oslo, Institute of Basic Medical Sciences, Norway.
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227
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Oakley RA, Lefcort FB, Plouffe P, Ritter A, Frank E. Neurotrophin-3 promotes the survival of a limited subpopulation of cutaneous sensory neurons. Dev Biol 2000; 224:415-27. [PMID: 10926777 DOI: 10.1006/dbio.2000.9804] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In the chick embryo, exogenous neurotrophin-3 (NT3) is sufficient to promote the differentiation of proprioceptive afferents even in the absence of limb muscle targets. To determine if NT3 can promote the differentiation of this phenotype in afferents with cutaneous targets, we analyzed the effects of chronic NT3 on cutaneous and muscle sensory neurons that express trkC, a receptor for NT3. In normal embryos, retrograde labeling and immunohistochemistry showed that about 75% of large-diameter muscle afferents express trkC, whereas only about 7% of large-diameter cutaneous afferents express this protein. After chronic treatment with NT3 during the cell death period, both populations of trkC(+) neurons were increased approximately twofold. Because this treatment is known to block cell death in sensory neurons, these results indicate that NT3 can promote the survival of both proprioceptive afferents and cutaneous afferents. To examine the phenotype of the cutaneous afferents rescued by NT3, we analyzed their projections and connections using transganglionic labeling and electrophysiological recording. The results indicate that exogenous NT3 neither altered the pattern of spinal projections nor caused cutaneous afferents to form monosynaptic connections with motor neurons. These results demonstrate that selective cell death does not contribute to the modality-specific pattern of spinal innervation and suggest that proprioceptive afferents may innervate muscle selectively.
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Affiliation(s)
- R A Oakley
- Department of Neurobiology, University of Pittsburgh, Pennsylvania 15261, USA
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228
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Sharma K, Leonard AE, Lettieri K, Pfaff SL. Genetic and epigenetic mechanisms contribute to motor neuron pathfinding. Nature 2000; 406:515-9. [PMID: 10952312 DOI: 10.1038/35020078] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Many lines of evidence indicate that genetically distinct subtypes of motor neurons are specified during development, with each type having characteristic properties of axon guidance and cell-body migration. Motor neuron subtypes express unique combinations of LIM-type homeodomain factors that may act as intrinsic genetic regulators of the cytoskeletal events that mediate cell migration, axon navigation or both. Although experimentally displaced motor neurons can pioneer new routes to their targets, in many cases the axons of motor neurons in complete isolation from their normal territories passively follow stereotypical pathways dictated by the environment. To investigate the nonspecific versus genetically controlled regulation of motor connectivity we forced all motor neurons to express ectopically a LIM gene combination appropriate for the subgroup that innervates axial muscles. Here we show that this genetic alteration is sufficient to convert the cell body settling pattern, gene-expression profile and axonal projections of all motor neurons to that of the axial subclass. Nevertheless, elevated occupancy of the axial pathway can override their genetic program, causing some axons to project to alternative targets.
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Affiliation(s)
- K Sharma
- Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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229
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Abstract
The central nervous system (CNS) is divided into diverse embryological and functional compartments. The early embryonic CNS consists of a series of transverse subdivisions (neuromeres) and longitudinal domains. These embryonic subdivisions represent histogenetic fields in which neurons are born and aggregate in distinct cell groups (brain nuclei and layers). Different subsets of these aggregates become selectively connected by nerve fiber tracts and, finally, by synapses, thus forming the neural circuits of the functional systems in the CNS. Recent work has shown that 30 or more members of the cadherin family of morphoregulatory molecules are differentially expressed in the developing and mature brain at almost all stages of development. In a regionally specific fashion, most cadherins studied to date are expressed by the embryonic subdivisions of the early embryonic brain, by developing brain nuclei, cortical layers and regions, and by fiber tracts, neural circuits and synapses. Each cadherin shows a unique expression pattern that is distinct from that of other cadherins. Experimental evidence suggests that cadherins contribute to CNS regionalization, morphogenesis and fiber tract formation, possibly by conferring preferentially homotypic adhesiveness (or other types of interactions) between the diverse structural elements of the CNS. Cadherin-mediated adhesive specificity may thus provide a molecular code for early embryonic CNS regionalization as well as for the development and maintenance of functional structures in the CNS, from embryonic subdivisions to brain nuclei, cortical layers and neural circuits, down to the level of individual synapses.
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Affiliation(s)
- C Redies
- Institute of Anatomy, University of Essen Medical School, Hufelandstrasse 55, Germany.
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230
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Glial cell line-derived neurotrophic factor and developing mammalian motoneurons: regulation of programmed cell death among motoneuron subtypes. J Neurosci 2000. [PMID: 10864958 DOI: 10.1523/jneurosci.20-13-05001.2000] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Because of discrepancies in previous reports regarding the role of glial cell line-derived neurotrophic factor (GDNF) in motoneuron (MN) development and survival, we have reexamined MNs in GDNF-deficient mice and in mice exposed to increased GDNF after in utero treatment or in transgenic animals overexpressing GDNF under the control of the muscle-specific promoter myogenin (myo-GDNF). With the exception of oculomotor and abducens MNs, the survival of all other populations of spinal and cranial MNs were reduced in GDNF-deficient embryos and increased in myo-GDNF and in utero treated animals. By contrast, the survival of spinal sensory neurons in the dorsal root ganglion and spinal interneurons were not affected by any of the perturbations of GDNF availability. In wild-type control embryos, all brachial and lumbar MNs appear to express the GDNF receptors c-ret and GFRalpha1 and the MN markers ChAT, islet-1, and islet-2, whereas only a small subset express GFRalpha2. GDNF-dependent MNs that are lost in GDNF-deficient animals express ret/GFRalpha1/islet-1, whereas many surviving GDNF-independent MNs express ret/GFRalpha1/GFRalpha2 and islet-1/islet-2. This indicates that many GDNF-independent MNs are characterized by the presence of GFRalpha2/islet-2. It seems likely that the GDNF-independent population represent MNs that require other GDNF family members (neurturin, persephin, artemin) for their survival. GDNF-dependent and -independent MNs may reflect subtypes with distinct synaptic targets and afferent inputs.
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231
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Abstract
Glial cell-line derived neurotrophic factor (GDNF) and its relative neurturin (NTN) are potent trophic factors for motoneurons. They exert their biological effects by activating the RET tyrosine kinase in the presence of a glycosyl-phosphatidylinositol-linked co-receptor, either GFRalpha1 or GFRalpha2. By whole-mount in situ hybridization on embryonic mouse spinal cord, we demonstrate that whereas Ret is expressed by nearly all motoneurons, Gfra1 and Gfra2 exhibit complex and distinct patterns of expression. Most motoneurons purified from Gfra1 null mutant mice had lost their responsiveness to both GDNF and NTN. However, a minority of them ( approximately 25%) retained their ability to respond to both factors, perhaps because they express GFRalpha2. Surprisingly, Gfra2(-/-) motoneurons showed normal survival responses to both GDNF and NTN. Thus, GFRalpha1, but not GFRalpha2, is absolutely required for the survival response of a majority of motoneurons to both GDNF and NTN. In accordance with the phenotype of the mutant motoneurons observed in culture we found the loss of distinct groups of motoneurons, identified by several markers, in the Gfra1(-/-) spinal cords but no gross defects in the Gfra2(-/-) mutant. During their natural programmed cell death period, motoneurons in the Gfra1(-/-) mutant mice undertook increased apoptosis. Taken together these findings support the existence of subpopulations of motoneuron with different trophic requirements, some of them being dependent on the GDNF family.
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232
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Kania A, Johnson RL, Jessell TM. Coordinate roles for LIM homeobox genes in directing the dorsoventral trajectory of motor axons in the vertebrate limb. Cell 2000; 102:161-73. [PMID: 10943837 DOI: 10.1016/s0092-8674(00)00022-2] [Citation(s) in RCA: 232] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Motor neurons extend axons along specific trajectories, but the molecules that control their pathfinding remain poorly defined. We show that two LIM homeodomain transcription factors, Lim1 and Lmx1b, control the initial trajectory of motor axons in the developing mammalian limb. The expression of Lim1 by a lateral set of lateral motor column (LMC) neurons ensures that their axons select a dorsal trajectory in the limb. In a complementary manner, the expression of Lmx1b by dorsal limb mesenchymal cells controls the dorsal and ventral axonal trajectories of medial and lateral LMC neurons. In the absence of these two proteins, motor axons appear to select dorsal and ventral trajectories at random. Thus, LIM homeodomain proteins act within motor neurons and cells that guide motor axons to establish the fidelity of a binary choice in axonal trajectory.
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Affiliation(s)
- A Kania
- Howard Hughes Medical Institute, Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA
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233
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Certel SJ, Clyne PJ, Carlson JR, Johnson WA. Regulation of central neuron synaptic targeting by the Drosophila POU protein, Acj6. Development 2000; 127:2395-405. [PMID: 10804181 DOI: 10.1242/dev.127.11.2395] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Mutations in the Drosophila class IV POU domain gene, abnormal chemosensory jump 6 (acj6), have previously been shown to cause physiological deficits in odor sensitivity. However, loss of Acj6 function also has a severe detrimental effect upon coordinated larval and adult movement that cannot be explained by the simple loss in odorant detection. In addition to olfactory sensory neurons, Acj6 is expressed in a distinct subset of postmitotic interneurons in the central nervous system from late embryonic to adult stages. In the larval and adult brain, Acj6 is highly expressed in central brain, optic and antennal lobe neurons. Loss of Acj6 function in larval optic lobe neurons results in disorganized retinal axon targeting and synapse selection. Furthermore, the lamina neurons themselves exhibit disorganized synaptic arbors in the medulla of acj6 mutant pupal brains, suggesting that Acj6 may play a role in regulating synaptic connections or structure. To further test this hypothesis, we misexpressed two Acj6 isoforms in motor neurons where they are not normally found. The two Acj6 isoforms are produced from alternatively spliced acj6 transcripts, resulting in significant structural differences in the amino-terminal POU IV box. Acj6 misexpression caused marked alterations at the neuromuscular junction, with contrasting effects upon nerve terminal branching and synapse formation associated with specific Acj6 isoforms. Our results suggest that the class IV POU domain factor, Acj6, may play an important role in regulating synaptic target selection by central neurons and that the amino-terminal POU IV box is important for regulation of Acj6 activity.
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Affiliation(s)
- S J Certel
- Department of Physiology and Biophysics, University of Iowa, Iowa City, IA, USA
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234
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Arber S, Ladle DR, Lin JH, Frank E, Jessell TM. ETS gene Er81 controls the formation of functional connections between group Ia sensory afferents and motor neurons. Cell 2000; 101:485-98. [PMID: 10850491 DOI: 10.1016/s0092-8674(00)80859-4] [Citation(s) in RCA: 380] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The connections formed between sensory and motor neurons (MNs) play a critical role in the control of motor behavior. During development, the axons of proprioceptive sensory neurons project into the spinal cord and form both direct and indirect connections with MNs. Two ETS transcription factors, ER81 and PEA3, are expressed by developing proprioceptive neurons and MNs, raising the possibility that these genes are involved in the formation of sensory-motor connections. Er81 mutant mice exhibit a severe motor discoordination, yet the specification of MNs and induction of muscle spindles occurs normally. The motor defect in Er81 mutants results from a failure of group Ia proprioceptive afferents to form a discrete termination zone in the ventral spinal cord. As a consequence there is a dramatic reduction in the formation of direct connections between proprioceptive afferents and MNs. ER81 therefore controls a late step in the establishment of functional sensory-motor circuitry in the developing spinal cord.
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Affiliation(s)
- S Arber
- Department of Biochemistry and Molecular Biophysics, Center for Neurobiology and Behavior, Columbia University, New York, New York 10032, USA
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235
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Xu B, Zang K, Ruff NL, Zhang YA, McConnell SK, Stryker MP, Reichardt LF. Cortical degeneration in the absence of neurotrophin signaling: dendritic retraction and neuronal loss after removal of the receptor TrkB. Neuron 2000; 26:233-45. [PMID: 10798407 DOI: 10.1016/s0896-6273(00)81153-8] [Citation(s) in RCA: 219] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To examine functions of TrkB in the adult CNS, TrkB has been removed from neurons expressing CaMKII, primarily pyramidal neurons, using Cre-mediated recombination. A floxed trkB allele was designed so that neurons lacking TrkB express tau-beta-galactosidase. Following trkB deletion in pyramidal cells, their dendritic arbors are altered, and cortical layers II/III and V are compressed, after which there is an apparent loss of mutant neurons expressing the transcription factor SCIP but not of those expressing Otx-1. Loss of neurons expressing SCIP requires deletion of trkB within affected neurons; reduction of neuronal ER81 expression does not, suggesting both direct and indirect effects of TrkB loss. Thus, TrkB is required for the maintenance of specific populations of cells in the adult neocortex.
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Affiliation(s)
- B Xu
- Department of Physiology, Howard Hughes Medical Institute, University of California, San Francisco 94143, USA
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236
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Glover JC. Development of specific connectivity between premotor neurons and motoneurons in the brain stem and spinal cord. Physiol Rev 2000; 80:615-47. [PMID: 10747203 DOI: 10.1152/physrev.2000.80.2.615] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Astounding progress has been made during the past decade in understanding the general principles governing the development of the nervous system. An area of prime physiological interest that is being elucidated is how the neural circuitry that governs movement is established. The concerted application of molecular biological, anatomical, and electrophysiological techniques to this problem is yielding gratifying insight into how motoneuron, interneuron, and sensory neuron identities are determined, how these different neuron types establish specific axonal projections, and how they recognize and synapse upon each other in patterns that enable the nervous system to exercise precise control over skeletal musculature. This review is an attempt to convey to the physiologist some of the exciting discoveries that have been made, within a context that is intended to link molecular mechanism to behavioral realization. The focus is restricted to the development of monosynaptic connections onto skeletal motoneurons. Principal topics include the inductive mechanisms that pattern the placement and differentiation of motoneurons, Ia sensory afferents, and premotor interneurons; the molecular guidance mechanisms that pattern the projection of premotor axons in the brain stem and spinal cord; and the precision with which initial synaptic connections onto motoneurons are established, with emphasis on the relative roles played by cellular recognition versus electrical activity. It is hoped that this review will provide a guide to understanding both the existing literature and the advances that await this rapidly developing topic.
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Affiliation(s)
- J C Glover
- Department of Anatomy, University of Oslo, Oslo, Norway.
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237
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Patel TD, Jackman A, Rice FL, Kucera J, Snider WD. Development of sensory neurons in the absence of NGF/TrkA signaling in vivo. Neuron 2000; 25:345-57. [PMID: 10719890 DOI: 10.1016/s0896-6273(00)80899-5] [Citation(s) in RCA: 294] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The neurotrophin survival dependence of peripheral neurons in vitro is regulated by the proapoptotic BCL-2 homolog BAX. To study peripheral neuron development in the absence of neurotrophin signaling, we have generated mice that are double null for BAX and nerve growth factor (NGF), and BAX and the NGF receptor TrkA. All dorsal root ganglion (DRG) neurons that normally die in the absence of NGF/TrkA signaling survive if BAX is also eliminated. These neurons extend axons through the dorsal roots and collateral branches into the dorsal horn. In contrast, superficial cutaneous innervation is absent. Furthermore, rescued sensory neurons fail to express biochemical markers characteristic of the nociceptive phenotype. These findings establish that NGF/TrkA signaling regulates peripheral target field innervation and is required for the full phenotypic differentiation of sensory neurons.
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MESH Headings
- Animals
- Calcitonin Gene-Related Peptide/genetics
- Cell Count
- Cell Differentiation/drug effects
- Cell Survival/drug effects
- Cells, Cultured
- Female
- Ganglia, Spinal/cytology
- Ganglia, Spinal/embryology
- Gene Expression Regulation, Developmental
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Mutant Strains
- Nerve Growth Factor/pharmacology
- Neurons, Afferent/chemistry
- Neurons, Afferent/cytology
- Neurons, Afferent/physiology
- Phenotype
- Proto-Oncogene Proteins/genetics
- Proto-Oncogene Proteins c-bcl-2
- Receptor, trkA/genetics
- Signal Transduction/physiology
- Skin/innervation
- Spinal Cord/cytology
- Substance P/genetics
- bcl-2-Associated X Protein
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Affiliation(s)
- T D Patel
- University of North Carolina Neuroscience Center, University of North Carolina, Chapel Hill 27599, USA
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238
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Mikaels A, Livet J, Westphal H, De Lapeyrière O, Ernfors P. A dynamic regulation of GDNF-family receptors correlates with a specific trophic dependency of cranial motor neuron subpopulations during development. Eur J Neurosci 2000; 12:446-56. [PMID: 10712625 DOI: 10.1046/j.1460-9568.2000.00924.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Glial cell line-derived neurotrophic factor (GDNF) family ligands promote the survival of developing motor neurons in vivo and in vitro. However, not all neurons survive with any single ligand in culture and GDNF null mutant mice display only a partial motor neuron loss. An interesting possibility is that subpopulations of motor neurons based on their function and/or their myotopic organization require distinct members of GDNF family ligands. Because responsiveness to the different ligands depends on the expression of their cognate ligand-binding receptor we have herein addressed this issue by examining the expression of GDNF-family receptors (gfr) during development and in the adult in cranial motor nuclei subpopulations. We have furthermore examined the in vivo role of GDNF for cranial motor neuron subpopulations. The shared ret receptor was expressed in all somatic, branchial and visceral cranial embryonic motor nuclei examined, showing that they are all competent to respond to GDNF family ligands during development. At early stages of development both the GDNF receptor, gfralpha1, and the neurturin (NTN) receptor, gfralpha2, were expressed in the oculomotor, facial and spinal accessory, and only gfralpha1 in the trochlear, superior salivatory, trigeminal, hypoglossal and weakly in the dorsal motor nucleus of the vagus and the ambiguous nucleus. The abducens nucleus was negative for both gfralpha1 and gfralpha2. The artemin (ART) receptor, gfralpha3, was expressed only in the superior salivatory nucleus. A motor neuron subnuclei-specific expression of gfralpha1 and gfralpha2 was seen in the facial and trigeminal nuclei which corresponded to their dependence on GDNF in null mutant mice. We found that the expression was dynamic in these nuclei, which may reflect developmental changes in their trophic factor dependency. Analysis of GDNF null mutant mice revealed that the dynamic receptor expression is regulated by the ligand in vivo, indicating that the attainment of changes in dependency could be ligand induced. Our results indicate that specific GDNF family ligands support selective muscle-motor neuron circuits during development.
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Affiliation(s)
- A Mikaels
- Laboratory of Molecular Neurobiology, MBB, Karolinska Institute, S171 77 Stockholm, Sweden
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239
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Abstract
Considerable progress has been made in understanding how combinatorially expressed transcription factors control the development of neuronal subtypes in the fly and vertebrate central nervous systems. The mode of action of many of these factors has been conserved from invertebrates to vertebrates throughout evolution, such as the formation and regulation of specific transcriptional complexes, the utilization of repressors for maintaining specificity, and the use of phosphorylation as an important means for transiently altering transcriptional activity.
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Affiliation(s)
- L W Jurata
- Gene Expression Laboratory, The Salk Institute for Biological Studies, La Jolla, 92037, USA.
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240
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Kas K, Finger E, Grall F, Gu X, Akbarali Y, Boltax J, Weiss A, Oettgen P, Kapeller R, Libermann TA. ESE-3, a novel member of an epithelium-specific ets transcription factor subfamily, demonstrates different target gene specificity from ESE-1. J Biol Chem 2000; 275:2986-98. [PMID: 10644770 DOI: 10.1074/jbc.275.4.2986] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Most cancers originate as a result of aberrant gene expression in mainly glandular epithelial tissues leading to defects in epithelial cell differentiation. The latter is governed by distinct sets of transcriptional regulators. Here we report the characterization of epithelium-specific Ets factor, family member 3 (ESE-3), a novel member of the ESE subfamily of Ets transcription factors. ESE-3 shows highest homology to two other epithelium restricted Ets factors, ESE-1 and ESE-2. ESE-3, like ESE-1 and ESE-2, is exclusively expressed in a subset of epithelial cells with highest expression in glandular epithelium such as prostate, pancreas, salivary gland, and trachea. A potential role in branching morphogenesis is suggested, since ESE-3 transactivates the c-MET promoter via three high affinity binding sites. Additionally, ESE-3 binding to DNA sequences in the promoters of several glandular epithelium-specific genes suggests a role for ESE-3 in later stages of glandular epithelium differentiation. Although ESE-3 and ESE-1 bind with similar affinity to various Ets binding sites, ESE-3 and ESE-1 differ significantly in their ability to transactivate the promoters containing these sites. Our results support the notion that ESE-1, ESE-2, and ESE-3 represent a unique epithelium-specific subfamily of Ets factors that have critical but distinct functions in epithelial cell differentiation and proliferation.
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Affiliation(s)
- K Kas
- New England Baptist Bone and Joint Institute, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, Massachusetts 02115, USA
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241
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Hepatocyte growth factor/scatter factor is a neurotrophic survival factor for lumbar but not for other somatic motoneurons in the chick embryo. J Neurosci 2000. [PMID: 10627610 DOI: 10.1523/jneurosci.20-01-00326.2000] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Hepatocyte growth factor/scatter factor (HGF/SF) is expressed in the developing limb muscles of the chick embryo during the period of spinal motoneuron (MN) programmed cell death, and its receptor c-met is expressed in lumbar MNs during this same period. Although cultured motoneurons from brachial, thoracic, and lumbar segments are all rescued from cell death by chick embryo muscle extract (CMX) as well as by other specific trophic agents, HGF/SF only promotes the survival of lumbar MNs. Similarly, treatment of embryos in ovo with exogenous HGF/SF rescues lumbar but not other somatic MNs from cell death. Blocking antibodies to HGF/SF (anti-HGF) reduce the effects of CMX on MN survival in vitro and decrease the number of lumbar MNs in vivo. The expression of c-met on MNs in vivo is regulated by a limb-derived trophic signal distinct from HGF/SF. HGF/SF is a potent, select, and physiologically relevant survival factor for a subpopulation of developing spinal MNs in the lumbar segments of the chick embryo.
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242
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Hoover F, Kielland A, Glover JC. RXR? gene is expressed by discrete cell columns within the alar plate of the brainstem of the chicken embryo. J Comp Neurol 2000. [DOI: 10.1002/(sici)1096-9861(20000124)416:4<417::aid-cne1>3.0.co;2-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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243
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Wolpowitz D, Mason TB, Dietrich P, Mendelsohn M, Talmage DA, Role LW. Cysteine-rich domain isoforms of the neuregulin-1 gene are required for maintenance of peripheral synapses. Neuron 2000; 25:79-91. [PMID: 10707974 DOI: 10.1016/s0896-6273(00)80873-9] [Citation(s) in RCA: 236] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Neuregulin-1 (NRG-1) signaling has been implicated in inductive interactions between pre- and postsynaptic partners during synaptogenesis. We used gene targeting to selectively disrupt cysteine-rich domain-(CRD-) containing NRG-1 isoforms. In CRD-NRG-1-/-mice, peripheral projections defasciculated and displayed aberrant branching patterns within their targets. Motor nerve terminals were transiently associated with broad bands of postsynaptic ACh receptor (AChR) clusters. Initially, Schwann cell precursors accompanied peripheral projections, but later, Schwann cells were absent from axons in the periphery. Following initial stages of synapse formation, sensory and motor nerves withdrew and degenerated. Our data demonstrate the essential role of CRD-NRG-1-mediated signaling for coordinating nerve, target, and Schwann cell interactions in the normal maintenance of peripheral synapses, and ultimately in the survival of CRD-NRG-1-expressing neurons.
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Affiliation(s)
- D Wolpowitz
- Columbia University, College of Physicians and Surgeons, Program in Neurobiology and Behavior, New York, New York 10032, USA
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244
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The ETS domain factor Pet-1 is an early and precise marker of central serotonin neurons and interacts with a conserved element in serotonergic genes. J Neurosci 1999. [PMID: 10575032 DOI: 10.1523/jneurosci.19-23-10348.1999] [Citation(s) in RCA: 204] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Serotonin (5-HT) plays a crucial neuromodulatory role in numerous physiological and behavioral functions, and dysfunction of the serotonergic system has been implicated in several psychiatric disorders. Despite the widespread importance of the central serotonergic neurotransmitter system, little is known about the molecular mechanisms controlling the development of 5-HT neurons. We previously identified an ETS domain transcription factor, Pet-1, that is expressed in a small number of tissues, including the brain. Here, we show that expression of Pet-1 RNA in the brain is restricted to, and marks, the entire rostrocaudal extent of rat serotonergic hindbrain raphe nuclei. Remarkably, Pet-1 RNA colocalizes with tryptophan hydroxylase-positive neurons in raphe nuclei but not with their nonserotonergic neuron or non-neuronal neighbors. Pet-1 RNA is limited to two domains in the developing hindbrain, which precedes the appearance of 5-HT in each domain by approximately a half day. Conserved Pet-1 binding sites are present in or near the promoter regions of the human and mouse 5-HT1a receptor, serotonin transporter, tryptophan hydroxylase, and aromatic L-amino acid decarboxylase genes whose expression is characteristic of the serotonergic neuron phenotype. These sites are capable of supporting transcriptional activation through interactions with the Pet-1 ETS domain and can function as enhancers. Together, our findings establish Pet-1 as an early and precise marker of 5-HT neurons and suggest that it functions specifically in the differentiation and maintenance of these neurons.
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245
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Gould TW, Burek MJ, Sosnowski JM, Prevette D, Oppenheim RW. The spatial-temporal gradient of naturally occurring motoneuron death reflects the time of prior exit from the cell cycle and position within the lateral motor column. Dev Biol 1999; 216:611-21. [PMID: 10642796 DOI: 10.1006/dbio.1999.9490] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Embryonic lumbar spinal motoneurons (MNs) are characterized by a period of programmed cell death (PCD) that spans several days and occurs in a rostrocaudal gradient. The generation of these MNs also takes place in a temporal-spatial gradient, such that MNs within rostral lumbar segments exit the cell cycle earlier and MNs within progressively caudal regions are born later. In vitro studies have shown that the latest born spinal MNs, presumably through the possession of endogenous "survival properties," are also the last to acquire their trophic dependence. If the birth date and therefore spinal cord location of lumbar spinal MNs influence the spatial-temporal pattern of PCD, then earlier born MNs should die sooner and be located more rostrally than those generated later. Alternatively, if the time at which MNs die during development is unrelated to their prior exit from the cell cycle, those born at various phases should die throughout the period of PCD. We report here that lumbar MNs generated during the earliest part (embryonic day 2-3) of the proliferative period in the developing chick spinal cord tend to die during the earliest stages of the PCD period and that MNs born in successive 12-h intervals die at correspondingly later periods during PCD. Furthermore, the spatial progression of PCD of these subpopulations of MNs occurs in a rostrocaudal gradient. Finally, while MNs do appear to die in a mediolateral gradient during the period of MN PCD, this pattern is only partly accounted for by MNs born in consecutive intervals. These data support the notion that the timing and rostrocaudal location of MNs undergoing PCD reflect their time of exit from the cell cycle.
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Affiliation(s)
- T W Gould
- Department of Neurobiology and Anatomy, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA
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246
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Weimann JM, Zhang YA, Levin ME, Devine WP, Brûlet P, McConnell SK. Cortical neurons require Otx1 for the refinement of exuberant axonal projections to subcortical targets. Neuron 1999; 24:819-31. [PMID: 10624946 DOI: 10.1016/s0896-6273(00)81030-2] [Citation(s) in RCA: 170] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Information processing in the nervous system depends on the creation of specific synaptic connections between neurons and targets during development. The homeodomain transcription factor Otx1 is expressed in early-generated neurons of the developing cerebral cortex. Within layer 5, Otx1 is expressed by neurons with subcortical axonal projections to the midbrain and spinal cord. Otx1 is also expressed in the precursors of these neurons, but is localized to the cytoplasm. Nuclear translocation of Otx1 occurs when layer 5 neurons enter a period of axonal refinement and eliminate a subset of their long-distance projections. Otx1 mutant mice are defective in the refinement of these exuberant projections, suggesting that Otx1 is required for the development of normal axonal connectivity and the generation of coordinated motor behavior.
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Affiliation(s)
- J M Weimann
- Department of Biological Sciences, Stanford University, California 94305-5020, USA
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247
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Poiraud E, Gruszczynski C, Porteu A, Cambier H, Escurat M, Koulakoff A, Kahn A, Berwald-Netter Y, Gautron S. The Na-G ion channel is transcribed from a single promoter controlled by distinct neuron- and Schwann cell-specific DNA elements. J Neurochem 1999; 73:2575-85. [PMID: 10582621 DOI: 10.1046/j.1471-4159.1999.0732575.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Na-G is a putative sodium (or cationic) channel expressed in neurons and glia of the PNS, in restricted neuronal subpopulations of the brain, and in several tissues outside the nervous system, like lung and adrenal medulla. To analyze the mechanisms underlying tissue-specific expression of this channel, we isolated the 5' region of the corresponding gene and show that Na-G mRNA transcription proceeds from a single promoter with multiple initiation sites. By transgenic mice studies, we demonstrate that 600 bp containing the Na-G proximal promoter region and the first exon are sufficient to drive the expression of a beta-galactosidase reporter gene in neurons of both CNS and PNS, whereas expression in Schwann cells depends on more remote DNA elements lying in the region between -6,500 and -1,050 bp upstream of the main transcription initiation sites. Crucial elements for lung-specific expression seem to be located in the region between -1,050 and -375 bp upstream of the promoter. Using in vivo footprint experiments, we demonstrate that several sites of the Na-G proximal promoter region are bound specifically by nuclear proteins in dorsal root ganglion neurons, as compared with nonexpressing hepatoma cells.
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MESH Headings
- Animals
- Base Sequence
- Central Nervous System/metabolism
- DNA Footprinting
- DNA, Complementary/genetics
- Exons/genetics
- Ganglia, Spinal/metabolism
- Genes, Reporter
- Liver/metabolism
- Lung/metabolism
- Mice
- Mice, Transgenic
- Molecular Sequence Data
- Muscles/metabolism
- Nerve Tissue Proteins/biosynthesis
- Nerve Tissue Proteins/genetics
- Neurons/metabolism
- Neurons, Afferent/metabolism
- Nuclear Proteins/metabolism
- Organ Specificity
- Peripheral Nervous System/metabolism
- Promoter Regions, Genetic
- RNA, Messenger/biosynthesis
- Rats
- Rats, Inbred F344
- Recombinant Fusion Proteins/biosynthesis
- Regulatory Sequences, Nucleic Acid
- Schwann Cells/metabolism
- Sodium Channels/biosynthesis
- Sodium Channels/genetics
- Transcription, Genetic
- Voltage-Gated Sodium Channels
- beta-Galactosidase/biosynthesis
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Affiliation(s)
- E Poiraud
- Biochimie Cellulaire, CNRS UPR 9065, Collège de France, Paris
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248
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Ritter AM, Frank E. Peripheral specification of Ia synaptic input to motoneurons innervating foreign target muscles. JOURNAL OF NEUROBIOLOGY 1999; 41:471-81. [PMID: 10590171 DOI: 10.1002/(sici)1097-4695(199912)41:4<471::aid-neu3>3.0.co;2-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Muscle sensory neurons, called Ia afferents, make monosynaptic connections with functionally related sets of motoneurons in the spinal cord. Previous work has suggested that peripheral target muscles play a major role in determining the central connections of Ia afferents with motoneurons. Here, we ask whether motoneurons can also be influenced by their target muscles in terms of the monosynaptic input they receive from Ia afferents, by transplanting thoracic motoneurons into the lumbosacral spinal cord so that they innervate foreign muscles. Three or four segments of thoracic neural tube from stage 14-15 chicken embryos were transplanted to the lumbosacral region of stage 16-17 embryos, and electrophysiological recordings were made from transplanted motoneurons after the embryos had reached stage 38-40. Transplanted thoracic motoneurons innervated limb muscles and received monosynaptic inputs from Ia afferents. These connections were not random: Most of the connections were formed between Ia afferents and motoneurons projecting to the same muscle (homonymous connections). Few aberrant connections were found although the anatomical distribution of afferents in the transplant indicated that they had ample opportunity to contact inappropriate motoneurons. We conclude that although peripheral target cues are not sufficient to respecify an already committed motoneuron (turn a thoracic motoneuron into a lumbosacral motoneuron), they do provide sufficient information for Ia afferent input to be functionally correct.
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Affiliation(s)
- A M Ritter
- Department of Neurobiology, University of Pittsburgh School of Medicine, BST W1413, 3500 Terrace Street, Pittsburgh, Pennsylvania 15261, USA
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249
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Abstract
The development of motor behaviour depends on the differentiation of underlying circuitry. Recent work with the zebrafish brings the simple swimming behaviour of lower vertebrates and their embryos into focus as a suitable model to study the development of motor circuitry and its genetic control. Changes in connectivity and excitability contribute to the development of swimming in this simple system. In the chick embryo, limb motor circuitry is spontaneously active before motor axons reach their muscle targets, and it has properties in common with the spontaneously active networks in the retina. The early rhythmic activity responsible for embryonic movement is probably a generalised property of developing spinal networks that precedes, and may be required for, the completion of functional locomotor circuitry.
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Affiliation(s)
- M Bate
- Department of Zoology, University of Cambridge, Cambridge, CB2 3EJ, UK.
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250
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Abstract
In the grasshopper CNS, serotonergic growth cones cross the midline early in development and initiate expression of serotonin uptake activity, or SERT. To test if the midline contains an activity that induces SERT, cuts were made that separated serotonergic cell bodies from the midline. SERT activity is completely lost when the midline is separated but is then rescued by bath-applied FGF2 (fibroblast growth factor 2), which can activate the heartless FGF receptor. heartless is expressed specifically in serotonergic neurons. A candidate FGF-like molecule was identified that is expressed in a subset of midline glia. SERT-expressing severed growth cones continue to migrate to their correct targets, which indicates that by the time SERT is activated, the serotonergic growth cones are committed to target-directed growth.
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Affiliation(s)
- B G Condron
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville 22908, USA.
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